The overall goal of this research plan is to elucidate how the hippocampal and dentate neuroepithelium is converted from a simple epithelial layer to the complex adult structure. The development of the dentate gyrus is particularly unique because it involves the formation, during development, of an ectopic germinative zone that persists and continues to generate new neurons throughout adulthood in rodents and primates (including humans). There is increasing evidence that the dentate gyrus is dysgenic in a subset of patients with temporal lobe epilepsy. Thus, the study of the normal mechanisms of dentate gyrus development, and the relationship of these mechanisms to dysgenic anomalies, will be critically important to our understanding and management of patients in this group. While the neuroanatomic outline of dentate gyrus development is fairly well understood the mechanistic underpinnings of this process are virtually unknown. The primary hypothesis of the proposed research is that development of the dentate neuroepithelium and the dentate gyrus is regulated by a complex cascade of bHLH transcription factors that act as intrinsic cues controlling differentiation of dentate granule cells from their most primitive precursors. The secondary hypothesis is that wnts produced by the cortical hem serve as extrinsic cues that regulate dentate gyrus and granule cell development by acting through cell-cell signaling mechanisms. The specific aims of the proposed research are: l) to characterize the function of the bHLH protein Mash1 in the production of dentate gyrus precursor cells and the development of dentate granule cells; 2) to identify the function of the normal cascade of bHLH proteins in the terminal differentiation of dentate granule cells and the organization of the dentate gyrus;.3) to determine the function of wnts in formation of the dentate gyrus. Experimental design and methods to accomplish the first two of these aims include the use of genetically modified mouse lines, in utero intraventricular retroviral injections and histologic analysis to characterize the function of Mash1 and other bHLH proteins in dentate gyrus development. The final aim consists of expression analysis of wnts, wnt receptors and wnt-inhibitory proteins and the use of cortical explants to understand the function of wnts in hippocampal development. The experiments described in the research plan should allow a detailed account of some intrinsic and extrinsic cues that control the cell fate of dentate granule cells and, hopefully, on the developmental basis of dentate gyrus dysgenesis in humans.